Wireless networks are increasingly employed to provide various communication functions including voice, video, packet data, messaging and the like. A wireless network such as a wireless local area networks (WLAN) may include any number of access points (APs) and any number of stations (STAs). An access point may act as a coordinator for communication with the stations. A station may actively communicate with an access point, may be idle, or may be powered down at any given moment depending on the data requirements of the station. Particularly with regard to mobile devices and other devices that are battery powered, minimizing energy consumption is an important aspect in the design of such systems. To that end, wireless communication systems typically include various power saving techniques that generally seek to increase the amount of time spent in a power save mode.
For example, within the IEEE 802.11 standards established by The Institute of Electrical and Electronics Engineers are provisions to allow a station to enter a low power mode of operation, also known as sleep mode, to save power. A STA may asynchronously signal that it is entering a power save mode through the use of a power management message contained in a packet sent to the AP. Upon receipt of a power management message indicating the STA is in power save mode, the AP may buffer packets to be sent to the STA. The AP periodically transmits beacons with a traffic indication message that may be used to indicate that data is ready to be transmitted to the STA. The period of time between beacon transmissions may be termed the beacon interval. The STA generally utilizes a period of time called the listen interval, corresponding to a plurality of beacon intervals, to coordinate its power save with the AP. The AP buffers data for the STA during the listen interval and the STA may awaken from power save mode to receive the beacon at the end of each listen interval. If the beacon indicates data is pending, the STA will initiate transfer of that data. Conversely, if no data is ready to be transmitted, the STA may return to power save mode.
As will be appreciated, proper coordination should be maintained between the AP and the STA to ensure that data is sent during periods when the STA is awake and able to actively receive the information, otherwise the information may need to be resent, consuming additional network resources, or worse, may be lost. In particular, an aspect of the above power save technique is that the power management bit is processed at the media access control (MAC) layer of the AP. There is a latency associated with operations occurring at the MAC layer, particularly as compared to operations occurring at lower levels, such as the hardware physical (PHY) layer. As a result, the PHY layer may have frames already queued for delivery to the STA when the MAC layer processes the power management bit. In turn, the one or more frames queued for delivery in the hardware may be transmitted to the STA. However, since the STA may go to sleep as soon as it sends the frame with the power management bit set, the STA may not receive the one or more frames subsequently sent from the hardware queue. Typically, the AP may retry transmitting the frames multiple times, consuming bandwidth. Ultimately, the frames may be dropped, further degrading performance.
Therefore, there remains a need to provide systems and methods for improving coordination of the operation of a device in power save mode to facilitate transfer of information. This invention accomplishes these and other goals.